View finder for zoom lens



'"" SEARCH ROOM 5 Sheets-Sheet 1 Original Filed Dec. 6, 1955 INVEN TORSATTO R N EYS July 19, 1960 E. w. BECHTOLD ETAL 2,945,415

vrsw FINDER FOR ZOOM LENS Original Filed Dec. 6, 1955 5 Sheets-Sheet 2IN VEN TORS [DWI/V W 55: mm

MARY/ V kAP/LOW JLEX J. WE/A/JI'I/N' ATTOQNLYS July 19, 1960 E. w.BECHTOLD EI'AL 2,945,415

vrsw FINDER FOR zoou uzus Original Filed Dec. 6, 1955 5 Sheets-Sheet 3 8D a mm w M my? a V C PW n mum n WMJ m July 19, 1960 E. w. BECHTOLD ETAL2,945,415

VIEW FINDER FOR ZOOM LENS Original Filed Dec'. 6, 1955 5 Sheets-Sheet 4v INVENTORS [DWI/V W. BECHTOID ATT-QlI-NLY5 July 19, 1960 E. w. BECHTOLDEI'AL 2,945,415

vnzw FINDER FOR zoom ums Original Filed Dec. 6, 1955 5 Sheets-Sheet 5FIG. \0.

FIG. 9. Y

INVENTORS ATT RNEY5 EDWIN w BECHTOLD v United States Patent VIEW FORZOOM LENS Edwin W. Bechtold, MiddleVillage, Marvin Kapilow, Peekskill,and Alex J. Weinstein, Mount Vernon, N.Y., assignors to The EdnaliteOptical Company, Inc., Peekskill, N.Y., a corporation of New YorkOriginal application Dec. 6 1955 Ser. No. 551,302. Divided and thisapplication May 31, 1957, Ser. No. 662,731

2 Claims. (Cl. 88--l.5)

This invention relates generally to lens systems for cameras, and isparticularly directed to a variable effective focal length lens systemfor movie cameras which produces the zoom effect of camera movementtoward and away from the object, without movement of the camera.

While there are devices in the prior art for producing the zoom effectby varying magnification of the image or equivalent focal length, suchdevices are subject to numerous inherent difficulties which haveprecluded thelr widespread acceptance. By way of example, prior zoomeffect lens systems required complex and delicate mechanisms for movingthe component lenses relative to each other. Further, a multiplicity ofoptical components or lenses were involved, and these lenses wererelatively expensive as being necessarily corrected for all positions ofmovement. For these and other reasons, previous zoom effect lens systemswere extremely costly to produce, unreliable in operation, and readilysusceptible to excessive wear which impaired the quality of image andreduced the range of magnification.

It is therefore a general object of the present invention to provide azoom effect lens system which overcomes the abovementioneddisadvantages, produces excellent quality images over a wide range ofmagnification with any camera, employs a highly simplified opticalsystem requiring a minimum of lenses, and which is extremely simple andinexpensive in construction, and accurate and reliable in use.

It is another object of the present invention to provide a manuallyactuable variable focal or zoom lens which produces a linear rate ofchange in magnification in response to a linear hand motion fornatural-appearing zoom effects.

it is another object of the present invention to provide an opticalconstruction having relatively movable lenses, wherein novel means areincluded to insure free lens movement and effectively reduce wear onmoving parts. More particularly, a feature of the present inventionprevents wedging, canting or cocking of a lens mount in a barrel ortube; and, in addition, permits relative movement of two or more lensmounts into and out of close proximity with each other.

It is another object of the present invention to provide a plurality ofseparate and distinct lens systems each having relatively movablelenses, and including novel means serving to move the lenses of theseveral systems in predetermined relation with respect to each other.

It is a further object of the present invention to provide an improvedviewfinder for use with zoom effect lens systems, which viewfinder issimple and rugged in construction, and automatically cooperates with itsassociated zoom lens to produce an image corresponding in magnificationto that of the zoom lens at all times.

Other objects of the present invention will become apparent upon readingthe following specification and referring to the accompanying drawings,which form a material part of this disclosure.

ice

construction, combinations of elements, and arrangements of parts, whichwill be exemplified in the construction hereinafter described, and ofwhich the scope will be indicated by the appended claims.

In the drawings:

Figure 1 is a plan view showing an accessory zoom lens and viewfinderconsrtucted in accordance with the present invention;

Fig. 2 is an enlarged, generally horizontal sectional view taken throughthe zoom lens of Fig. 1, with the parts thereof in an intermediate ornormal position;

Fig. 3 is a partial, vertical sectional view taken substantially alongthe line 33 of Fig. 1;

Fig. 4 is an enlarged, generally horizontal sectional view taken throughthe viewfinder of Fig. 1, with the parts in a normal or intermediateposition corresponding to that of Fig. 2;

Fig. 5 is a transverse sectional view taken generally along the line 5-5of Fig. 1 or Fig. 2;

Fig. 6 is an optical ray diagram schematically illustrating the opticalsystems of the instant zoom lens and viewfinder in their extreme wideangle positions of minimum effective focal length and fractionalmagnification, without attempted accuracy of geometry or lens shapes;

Fig. 7 is a ray diagram similar to Fig. 6, but showing the opticalcomponents in an intermediate or normal position of unit magnificationwith no enlargement or reduction of image size;

Fig. 8 is an optical ray diagram similar to Figs. 6 and 7, but showingthe lens systems in their extreme telephoto positions of maximummagnification and efiective focal length;

Fig. 9 is a plan view showing a slightly modified form of accessory zoomlens and viewfinder of the present invention, with parts broken away forclarity of understanding;

Fig. 10 is an elevational view showing a range indicatord of the instantinvention, removed, from the assembly; an

Fig. 11 is a front elevational view of the embodiment of Fig. 9.

Referring now more particularly to the drawings, and specifically toFig. 1 thereof, the embodiment of the invention illustrated thereincomprises a zoom effect accessory lens, generally designated 10, a viewfinder, generally designated 11, which is arranged longitudinallyalongside of and fixedly secured to the accessory lens transverselyextending bracket 12. An operating arm lever or handle projectstransversely from the lens 10 for manually actuating the lens andviewfinder.

In Fig. 2 the zoom lens 10 is seen in greater detail,-

and includes a generally tubular barrel 15, a converging front lens orlens unit 16 mounted forwards in the barrel, and an intermediate,diverging lens or lens unit 18 mounted in the barrel between the frontand rear lenses. Also illustrated as mounted in the barrel 15, rearwardsof the rear lens 17, is an additional lens unit or assembly 19. However,the lens assembly 19 functions only as a conventional camera objectivelens; and, while it is preferred to replace the camera objective withthe entire accessory lens 10 of Fig. 2 to obtain zoom effects, it isappreciated that the lens assembly 19 could be omitted and the cameraobjective substituted in place of the latter assembly.

A tubular, open ended outer shell or body 22 constitutes one element ofthe barrel 15. The outer shell or body 22 is of generally cylindricalconfiguration, and is provided at its forward end with an external,peripheral enlargement 23 having external screw threads formed thereon.Spaced between the externally threaded enlargement 23 and the rear endof the outer shell 22 is a circumferentially extending, externalshoulder or collar 24. It will be noted that the peripheral enlargement23 and collar 24 combine with the external surface of the outer shell 22to define a circumferentially extending external groove or recess 25.

Formed internally of the outer shell or body 22 is a longitudinallyextending, inwardly o'pening recess guideway or groove 27. The groove 27is generally straight, as shown in dashed lines in Fig. 2, and may haveits opposite ends opening through opposite ends of the outer shell. Justrearwards of the external shoulder or collar 24, the outer shell or body22 is formed with a through slot 28,extending circumferentiallyapproximately 160 about the shell. In Fig. it will be observed that theslot or opening 28 terminates at one end just short of the groove 27.

Arranged longitudinally of and slidably within the outer shell or body22 is an open ended, generally cylindrical barrel liner or inner tube30. Formed in the liner wall, in substantial alignment with the slot 28of the outer shell 22, is an opening or bore 31, and in the rearwardportion of the cylindrical inner liner is a generally arcuate orcurvilinear closed end slot 32. The slot 32 extends approximately 139about the circumference of the inner liner, and has its intermediateregion disposed rearwards of its end regions. Forwards of the arcuateslot 32. the inner liner 30 is formed with a generally helical, closedend slot 33. More specifically, the slot 33 extends helically,approximately 139 about the axis of the liner 30, and has its oppositeends respectively in substantial alignment with the ends of the slot 32,longitudinally of the liner. Stated otherwise, the closed end slots 32and 33 are substantially coextensive with each other circumferentiallyof the liner 30.

Secured on the forward end of the barrel shell 22 is an o'pen endedbarrel element or focusing tube 36, which has its rearward portion 37internally threaded for engagement with the externally threadedenlargement 23 of the barrel shell. Further, the focusing tube 36 hasits intermediate portion 38 internally threaded for adjustably receivingthe lens unit 16, and also has its forward end portion 39 internallythreaded for releasably securing a dust cap (not shown) in closingrelation over the fo'rward barrel end. Projecting rearwards from thefocusing tube 36 and extending circumferentially about the barrel shell22, is an annular lip or skirt 40. A stop member or pin 41 extendsradially inwards through the skirt 40. being threadedly secured in thelatter, and extends into the external groove or recess 25 of the barrelshell 22. The pin 41 is thus movable with the focusing tube 36longitudinally of the barrel l5, and engageable with the machined sidesor side walls of the groove 25 to accurately limit rearward and forwardmovement of the focusing tube relative to the shell or body 22. Focusingtube adjustment is thus permitted over a relatively wide range,considerably greater than that possible within 360 rotation of the tube.

Circumpo'sed about the lip 40 and extending rearwards therefrom is acalibrated annular ring or scale 44 which is adjustably fixed to the lipby a set screw 45 or other suitable means. The rearward portion 37 ofthe focusing tube 36 may be externally knurled as at 46. to facilitateits manual rotation; and the ring 44 is preferably calibrated in objectdistances, and selectively positionable with respect to a mark on thebarrel shell 22, as seen in Fig. l.

Rotatably circumpo'sed about the barrel shell 22. overlying the slot 28,is an externally toothed drive ring or gear 47. A drive pin or peg 48 isthreadedly engaged inwards through the ring 47, and extends spacedlythrough the barrel shell slot 28. having its inner end snugly receivedin the liner bore 31. The liner 30 and drive ring 47 are thereby fixedlyconnected together for simultaneous axial rotation relative to thebarrel shell 22 and within the limits defined by the slot 28. Oppo'siteto the pin 48, the arm or handle 13 hasone end removably secured inthreaded engagement within a boss or lug 49, which is in turn threadedlysecured in the drive gear 47.

Fixedly clamped about, or otherwise secured to the barrel shell 22. justrearwards of the rotatable drive gear 47. is one end portion 52 of thebracket 12. An end cap 54 is engaged over the rear end of the barrelshell 22 and fixedly positioned on the latter by one or more set screws55. The endcap 54 carries the optional camera objective lens unit 19,and also preferably carries a variable iris or aperture mechanism,diagrammatically presented at 56. Rotatably circumposed about the endcap 54 is an externally knurled. iris actuating ring 57. best seen inFig. 3. A drive pin 58 extends inwards from the iris actuating ring 57,through the end cap 54, and is operatively connected to the irismechanism 56 to vary the aperture upon rotation of the iris ring. In theconventional manner, a spring pressed detent ball 59 may be mounted inthe iris ring 57 and engageable with the end cap 54 to releasably retainthe iris ring in any selected position of its rotation.

Detachably fixed on the rearward end of the end cap 54 is an externallythreaded mounting ring 60 adapted for threaded engagement in a cameralens o'pening. More particularly, the mounting ring 60 is circumposedabout the rearward portion of the end cap 54 and firmly retained on theend cap by a plurality of set screws 61 engaging in angular recesses ofthe end cap. A radial flange 62 on the mounting ring 60 retains the irisactuating ring 57 in position on the end cap.

The converging front lens unit 16 includes an annular mount or ring 65externally threaded for engagement with the internal screw threads ofthe intermediate focusing tube portion 38. Thus, the mounting ring 65 isaxially adjustable in the focusing tube 36 and may be fixed at theproper position of adjustment by one or more set screws 66 extendinginwards throughthe focusing tube. The lens proper 67 of the lens unit 16is of plus or positive power, commonly called a converging lens, and maybe composed of more than one lens element to obtain the desiredcorrection. An externally threaded lock nut or retaining ring 68 securesthe lens 67 in its mount 65.

The rear converging lens unit 17 includes a lens mounting annulus orring 70 slidably received in the rearward portion of the barrel liner30; and, the mounting ring is provided about its circumference with aplurality of peripheral openings or notches 71, see Fig. 5. Four suchopenings are shown for purposes of illustration. A plurality ofcircumferentially spaced, elongate tongues or slide bars 72 projectforwards from the mounting ring 70. longitudinally of the liner 30. andin slidable engagement with the interior surface of the latter. In Fig.5 it will be noted that four tongues or slide bars 72 are disposedrespectively adjacent to and offset from the ring notches 71. However,it is appreciated that more or less tongues 2 may be employed, asdesired, and that their number need not correspond to the number ofnotches.

As the tongues 72 slidably engage with the internal surface of the liner30, they reduce the unit bearing pressure of the mounting ring 70 on thebarrel liner, thereby minimizing wear of the bearing surfaces. Furtherthe longitudinal or axial extension of the slide bars 72 serves toincrease the effective axial dimension of the mounting ring 70 and thusprevent canting or tilting of the latter. That is, canting of themounting ring 70 is prevented, so that the ring cannot wedge or cock inthe liner and jam or score the moving parts.

The lens proper 73 of the rear lens unit 17 is also a plus or converginglens. and is secured in the ring 70 by an externally threaded retainingring or lock nut 74. Projecting radially outwards from the mounting ring70 is a cam follower. pin or lug 76, best seen in Fig. 5, which extendsthrough the barrel liner slot 32 and into the groove 27 of the barrelshell. In practice, the cam follower 76 may advantageously consist of aheaded screw or fastener 77 extending radially into the mounting ring70. I

It will now be understood that axial rotation of the barrel liner 30, aseffected by rotation of the drive ring 47, will shift the pin 76longitudinally of the barrel 15 along the barrel shell groove 27 asdetermined by the curvature of the slot 32. That is, the pin 76 isconfined in both the groove 27 and slot 32, and is thereby constrainedto movement longitudinally of the barrel, always being positioned at theintersection of the latter groove and slot. The bounding edge of theslot 32 thus defines a cam surface engaging the pin 76 to shift the lensunit 17 longitudinally within the barrel liner 30. As notedliereinbefore, the tongues 72 insure free sliding movement of the lensunit 17 in the barrel liner, with a minimum of wear.

The intermediate lens unit 18 includes a lens mounting annulus or ring80 disposed axially and slidably within the forward region of the barrelliner 30. Formed in the periphery of the mounting ring 80 are aplurality of circumferentially spaced notches or openings, which may beidentical to the notches 71 of the mounting ring 70, and are thereforenot shown in the drawings. It is essential. however, that the notches ofthe mounting ring 80 he in alignment, respectively, longitudinally ofthe barrel 15 with the tongues or slide bars 72 and of sufficient sizeto receive the latter, for purposes appearing presently.

A plurality of longitudinally extending tongues or slide bars 81 projectrem-wards from the lens mounting ring 80 toward the lens mounting ring70 in Fig. 2. The slide bars 81 are disposed in parallelism with eachother, circumfercntiully spaced about the mounting ring 80, and each inslidnble engagement with the interior surface of the barrel liner 30. inFig. 5 it will be observed that each of the slide bars 81 is inlongitudinal alignment with a respective one of the notches 71 of themounting ring 70, and of a cross sectional size to be received in itsrespective notch upon sliding movement of the mounting rings 70 and 80toward each other. That is, the slide bars 81 are circumferentiallyoffset from the slide bars 72 so as to be in alignment with the notches71' of the mounting ring 70. and similarly, the peripheral notches ofthe mounting ring 80 (not shown) are circumferentially offset from theguide bars 81 of the latter mounting ring so as to be in alignment withthe slide bars 72 for receiving the latter upon movement of the mountingrings 70 and 80 toward each other. By this construction, the mountingrings 70 and 80 may be moved into and out of close proximity with eachother.

The guide bars 81 slidably engage the interior surface of the barrelliner 30 and function in substantially the same manner as the guide bars72, namely, to reduce unit bearing pressure and wear, and to preventcanting or wedging of the mounting ring 80 in the barrel liner.

The lens proper 82 of the lens unit 18 is of negative or minus power,commonly called a diverging lens, and may be formed of a plurality ofcemented lens elements, as required for the desired correction. Forreasons appearing hereinafter in greater detail, the negative strengthor power of the diverging, intermediate lens 82 15 greater than thepositive strength or power of either the front converging lens 67 or therear converging lens 73. An externally threaded lock nut or retainingring 83 15 engaged interiorly of the mounting ring 80 to secure the lens82 in the latter mounting ring.

Projecting radially outwards from the periphery of the lens mountingring 80 is a cam follower lug or pin 84, shown in dashed outline in Fig.2, and which may in practice constitute the head of a threaded fastenersuch as was described in connection with the cam follower 76. The camfollower 84 extends radially outwards through the helical barrel linerslot 33, being slidable therein, and is slidably received in thelongitudinal barrel shell groove 27. The cam follower 84 is thusconfined to movement within the slot 33 and groove 27. As the groove 27is fixed relative to barrel 15, the cam follower and hence the lens unit18 is constrained to longitudinal or axial movement relative to thebarrel, while the inclination or helix angle of the slot 33 determinesthe rate of axial movement of the lens unit for a given rate of barrelliner rotation and constrains the diverging lens unit to a predeterminedposition of axial movement for each position of barrel liner rotation.Hence, the bounding edge of the liner slot 33 defines a cam surfacewhich constrains the diverging lens unit to a predetermined axialmotion. As the liner cam slot 33 is preferably a true spiral or helix,axial movement of the diverging lens unit 18 will be directlyproportional to, or a liner function of rotative movement of the barrelliner 30 and drive ring 47.

It will now be understood that clockwise rotation of the operating leveror arm 13, as viewed in Fig. 5, will axially shift the lens units 18 and17 to their extreme position of movement toward each other. This may beappreciated by visualizing the cam slots 32 and 33 to move upwards, asseen in Fig. 2, thereby causing the cam follower 76 and its lens unit 17to shift leftwards and causing the cam follower 84 and its lens unit 18to shift rightwards. The illustrated position of Fig. 2 is a normal orintermediate position of unit magnification. Upon counter clockwiselever arm rotation, as seen in Fig. 5, both the intermediate ordiverging lens unit 18 and the rear converging lens unit 17 are shiftedforward, or leftward as seen in Fig. 2 to their extreme position ofmovement away from each other.

The construction of the viewfinder 11 is best seen in Fig. 4 as composedessentially of an open ended tubular barrel, generally designated 90,which is disposed longitudinally alongside of the zoom lens 10 andfixedly connected to the latter by the bracket 12. Axially mountedinteriorly of the viewfinder barrel are a front, converging viewfinderlens unit 91, an intermediate diverging viewfinder lens unit 92, and arear viewfinder lens unit or'eyepiece lens assembly 93.

The viewfinder barrel 11 includes an open ended, tubular outer shell orbody of generally cylindrical configuration and having its rearwardportion 96 of reduced external diameter. Spaced from the rear end of theviewfinder barrel shell 95, its reduced rearward portion 96 is formedwith a through slot 97 extending circumferentially about the shellapproximately 180". Generally opposite to the central region of thecircumferential slot 97, the barrel shell 95 is formed on its innersurface with a straight, longitudinally extending open ended groove orguideway 98. The forward portion of the shell 95 is interiorly enlarged,terminating in a forwardly facing shoulder 99 and provided with internalscrew threads 100.

Rotatably circumposed about the reduced rearward shell portion 96,overlying the circumferentially extending slot or opening 97 is anexternally toothed drive ring or gear 103. Extending radially inwardsfrom the drive ring 103, through and beyond the slot 97 is a drive pin104. This drive pin may be threadedly secured in the drive ring 103 andhave its inner end extend spacedly through and inwards beyond the slot97, for rotation with the drive ring within the limits of the slot.

Diametrically opposite to the drive pin 104, an in-- ternally threadedboss 105 is threaded or otherwise secured in the drive ring 103 andprojects radially outwards therefrom. The boss 105 is adapted tooptionally receive the operating lever 13, as for a left-handed operatoror otherwise when convenience requires.

An end portion or loop 106 of the bracket 12 is clamped about orotherwise fixedly secured to the barrel shell 95 just rearwards of therotatable drive ring 103.

The viewfinder barrel includes a cap-like rear end piece 108 engagedover the rear end of the barrel shell 95 and secured in position by oneor more set screws 109. In

particular. the barrel end piece 108 is of generally annularconfiguration. formed with internal screw threads 110 and provided witha rearwardly facing, eye engaging portion 111.

The front converging lens unit 95 of the viewfinder 11 includes a frontconverging lens 113. and a field of view window or mask 114. which aretogether clamped in position against the forwardly facing shell shoulder99 y an externally threaded lock nut or retaining ring 115. The openingin mask 114 is offset from center. as seen in Fig. 4. to compensate forparallax.

The intermediate viewfinder lens unit 92 includes a tubular lens mountarranged longitudinally within the barrel shell 95 and slidable forwardsand rearwards in the latter. The external surface of the tubular lensmount 117 is formed with a generally helical, outwardly opening guidewayor groove 118, which is shown in dot-and-dash outline extendingrearwards into the paper. The inner end of the pin 104 is slidablyreceived within the groove or opening 118. Projecting radially from thelens mounting tube 117 into the internal groove or guideway 98 of theshell 95. is a lug or pin 120. The lug 120 is slidably received in thelongitudinal groove 98. and may, as illustrated. constitute the enlargedend or head of a screw or fastener threadedly secured in the mountingtube 117.

The lens proper 122 of the intermediate lens unit 92 is of minus ornegative power. commonly called diverging. and is of greater minus poweror strength than the positive or plus strength of the front converginglens 113. It will be observed that the diverging lens 122 is secured inthe forward region of the lens mounting tube 117 by an externallythreaded lock nut or retaining ring 123 threadedly engaged in themounting tube.

Upon rotation of the drive ring or gear 103, the drive pin 104 willrotate circumferentially of the shell 95 in the slot 118 and tend tocause rotation of the lens mounting tube 117 by engagement of the drivepin in the helical groove 118. However, the lug 120 is slidable in thelongitudinal guideway or groove 98 to constrain the lens mounting tube117 to longitudinal shifting movement in the barrel shell 95. Rotationof the drive ring 103 therefore causes the pin 104 to slide in thegroove or guideway 118 and shift the lens unit 92 forwardly andrearwardly in the viewfinder barrel 90. Further, according to theinclination or helix angle of the helical groove 118, the lens mountingtube 117, and hence the diverging lens unit 92 moves at a predeterminedlinear rate for a given linear rate of drive ring rotation, and islocated longitudinally of the barrel shell 95 in correspondence with theangular disposition of the drive ring and pin.

The bracket 12 fixedly secures the accessory zoom lens 10 and viewfinder11 in laterally spaced apart relation, and rotatably supports a pinionor spur gear 133 in meshing engagement with both the drive gears 47 and103 of the accessory lens and viewfinder, respectively. Morespecifically. as seen in Fig. 4, the pinion 133 is journaled in theintermediate portion of the bracket 12 for rotation about an axisextending longitudinally of the zoom lens and viewfinder. A disc orbutton 134 holds the pinion 133 on the bracket 12. Through the pinion133, the drive ring 47 and lens units 17 and 18 of the zoom lens areoperatively connected to the drive ring 103 and viewfinder lens unit 92for movement in predetermined relation with respect to each other.Further, movement of the movable lens units of both the zoom lens andview-finder is effected by actuation of the lever 13.

In the schematic ray diagrams of Figs. 6. 7 and 8. the upper diagram ofeach figure corresponds to the optical system of the zoom lens 10. whilethe lower diagram of each figure corresponds to the optical system ofthe viewfinder 11. Fig. 6 illustrates the optical systems in theirextreme wide angle position of minimum effective focal length andfractional image magnification or reduction. wherein the drive gears 47and 103 have been rotated to their limiting counter clockwise positionto shift forward both the intermediate diverging zoom lens unit 18 andthe intermediate diverging viewfinder lens unit 92. The rear converginglens unit 17 of the zoom lens is also in a forward position.

In the normal position of zero magnification, i.e., no change in imagesize over that produced by the objective lens, the lens units of thezoom lens and viewfinder are in substantially the positions shown inFigs. 2, 4, and 7. The intermediate diverging lens units 17 and 92 areapproximately midway of their axial travel, and the rear converging lensunit 17 of the zoom lens system is at its rearmost position.

in Fig. 8, the telephoto condition of maximum effective focal length andimage magnification, is illustrated, wherein both the drive gears 47 and103 have been rotated to their limiting clockwise position, as seen inFig. 5, to shift the intermediate zoom lens unit 18 and intermediateviewfinder lens unit 92 to their rearmost positions. The rear converginglens unit 17 of the zoom lens system is simultaneously shifted forwardsinto close proximity to the diverging lens unit 18.

As the diverging lens 82 of the zoom eifcct lens system is of greaterstrength or power than either the front converging lens 67 or the rearconverging lens 73, the diverging lens combines with the converginglenses individually to define negative compound front and rear lenses.That is, in the wide angle condition of Fig. 6, the diverging lens 82and converging lens 67 combine to define a negative compound front lens,and in the telephoto condition of Fig. 8, the diverging lens 82 andconverging rear lens 73 combine to define a negative compound rear lens.

In the wide angle condition, the rear converging lens 73 is of suchpower and so spaced from the negative compound front lens as tocooperate with the latter to form an erect, diminished virtual image.The diverging lens 82 combines with the rear converging lens 73 in thetelephoto condition of Fig. 8 to define a negative, compound rear lenswhich is so spaced from the converging front lens 67 as to cooperatewith the latterto form an erect, enlarged virtual image. In thecondition of Fig. 7, the movable lenses 73 and 82 are so spaced relativeto each other and the fixed lens 67 as to neutralize each other anddefine an erect image of unit magnification. As movement of the lenses73 and 82 between the wide angle and telephoto conditions is gradual andcontinuous, a virtual, erect image of continually changing size will beformed.

In order to insure afocal magnification by the zoom lens system, whereinparallel rays entering through the front converging lens 67 emerge inparallelism from the rear converging lens 73, the latter lens isconstrained by the configuration of the cam slot 32 to movement suchthat it is always spaced by its focal length from the image formed bythe diverging lens 82. For purposes of explanation it may be assumedthat movement of the rear converging lens 73 plays no part in changingthe magnification of the system, but only maintains the system afocal.By this explanation, change in magnification is dependent only uponmovement of the diverging lens 82 relative to the converging front lens67.

As magnification varies directly with the distance between the diverginglens 82 and converging lens 67, and as the cam slot 33 is substantiallya true helix, it follows that change in magnification is substantiallylinear or varies directly with rotation of the drive gear 47.

By way of example, and Without intent to be limited thereto, lenses ofthe following characteristics have been satisfactorily employed in theinstant device:

Focal length Front converging lens 67 mm 66.7 Intermediate diverginglens 82 mm 21.5 Rear converging lens 73 mm" 66.7

Of course, a great variety of other lens combinations may be employed.For each such combination it will be necessary to calculate and plot thecurvature of the cam slot 32 necessary to constrain the rear converginglens to a position at a distance from the image formed by the diverginglens 82 equal to the focal length of the rear converging lens.

In practice a fully corrected and relatively inexpensive zoom effectlens system of the present invention has been produced by forming eachof the front converging lens 67 and the diverging lens 82 of twocemented lens elements, and framing the rear converging lens 73 of asingle element.

In order to focus the zoom effect lens system for objects at differentdistances, it is only necessary to rotate the focusing tube 36 relativeto the barrel shell 22 to place the desired graduation of scale 44, seeFig. 1, in alignment with a marking on the barrel shell portion 24.This, of course. changes the spacing between the front converging lens67 and diverging lens 82 for all positions of the latter lens. Initialsetting of the focus scale 44 may be made by adjusting the lens mountingring 65 in the focusing tube 36 to properly focus an object at infinity.and then rotating the scale 44 relative to the focusing tube 36 toproperly place the infinity marking. This is all done with the stop pin41 in abutting engagement with the shoulder 24, as seen in Fig. 2. Theset screws 66 and 45 may then be tightened, and the focusing tube 36 setfor any desired object distance.

Of course. the abovementioned magnification and demagnification ineffect changes the focal length of the camera objective. Therefore, itis preferred to graduate the drive ring 47 in effective focal lengths,see Fig. 1, so that the effective focal length may be determined for anyposition of the drive ring.

As the instant zoom lens system is preferably afocal, it follows thatthe system may be employed with any camera objective.

The schematic ray diagrams of Figs. 6, 7 and 8 also illustrate the wideangle, neutralized and telephoto conditions, respectively, of theviewfinder 11. In essence, the viewfinder lens system operates in amanner similar to that of the zoom effect lens system, the diverginglens 122 combining with the front converging lens 113 to define anegative compound front lens in the wide angle condition, and combiningwith the eyepiece lenses 128 and 129 to define a negative compound rearlens in the telephoto condition. However, for simplicity ofconstruction, the eyepiece lenses 128 and 129 are fixed in theviewfinder barrel 90, while only the diverging lens 122 is axiallymovable. Hence, the viewfinder lens system cannot be afocal for allpositions of diverging lens movement, but this is not essential as theoperator's eye can accommodate.

In the embodiment of Figs. 9 and II, a zoom effect accessory lens,generally designated 10', is arranged longitudinally along side of aviewfinder, generally designated 11 and fixedly secured to the latter bya trans-' versely extending bracket 13.

The zoom lens 10 is substantially the same as the hereinbefore describedzoom lens 10, with the exception of a drive ring or gear 47' is also ofthe spur type but is provided with a rearwardly facing peripheralshoulder, lip or ridge 150 which projects radially outwards beyond theteeth of the spur gear 47 and has its forward side beveled or chamfered,as at 151.

The viewfinder drive ring or gear 103' corresponding to the hereinbeforedescribed gear 103, is of similar construction to the gear 47', andformed with a rearwardly facing, forwardly beveled, peripheral lip orshoulder 153 projecting radially outwards beyond the teeth of the gear(not shown in the drawings).

The bracket 13', which corresponds to the bracket 13 of the firstdescribed form of the invention, differs from the latter by theprovision of a forwardly projecting periphe'ral skirt 155 which definesin the bracket 13' a forwardly opening recess for receiving the gears47' and 103', and the intermediate gear 133'. As shown in section inFig. 9, the forward edge of the bracket skirt 155 engages with therearwardly facing gear shoulder to enclose and protect the teeth of thegear 47. The forward edge of the skirt 55 is also engaged by therearwardly facing shoulder 153 of the viewfinder gear 103 to enclose andprotect the teeth of the latter gear; and, a cover plate 157 is fixedlysecured, as by fasteners 158, in abutting engagement with the forwardedge portions of bracket skirt 155 between the zoom lensand viewfinderto enclose and protect the intermediate gear 133'. That is, the coverplate 157 combines with the intermediate portion of the bracket 13 andengages with the forward, beveled sides of the gear shoulders 150 and153 to enclose the intermediate gear 133, while the bracket shirtportions extending about the zoom lens and viewfinder engage with theadjacent rearward surfaces of the 150 end. By this construction, thedrive gears 47 and 103. are completely enclosed and protected fromforeign matter by the bracket 13', cover plate 157 and gear shoulders150 and 153.

For convenience in operation, the disc or button 134' which correspondsto the disc 134, is fixed to the gear 133' for rotation therewith, andprovided with markings as in Fig. 10 readily observable by the operator.As appears. the disc or indicator button 134 is marked off in threesectors or zones 160, 161 and 162; and, cooperating markings areprovided on the rear surface of the bracket 13' (not shown). The discsectors 160, 161 and 162 may be marked in different colors, or byprinting, or both, to indicate when the lens system is in the wideangle, normal or telephoto zone or condition, and the approximate degreeof the particular condition.

As noted hereinbefore, the mask 114 of the viewfinder 11 is laterallyoffset to compensate for parallax. In Fig. 11 it will be observed thatthe mask 114 of the viewfinder 11 is also offset to compensate forparallax; and further, the mask 114 is provided with a notch or slot 165in one laterally extending edge of the mask opening, to compensate forthe increased parallax at the very short focusing distances permitted bythe stop arrangement of the focusing tube described hereinbefore. It ispreferred that the notch 165 be covered by a transparent, colored sheetso as to be easily distinguished from the picture being taken.

The present invention also contemplates the provision of a novel adaptorring 168 which has an exteriorly threaded inner portion 169 threadedlyengageable in and removable from the internally threaded barrel portion39. The adaptor ring 168 is formed with an internal, angular shoulder170 adjacent to and spaced from the rearward end of the ring, and hasits forward portion 171 circumferentially enlarged and provided withinternal screw threads 172 of substantially the same size as theinternal screw threads of the barrel portion 39. A filter 173 is adaptedto be releaseably clamped in the barrel 15 by the internal adaptor ringshoulder 170; and, the second filter 174 is adapted to be releaseablyclamped in the adaptor ring 168 between the internal shoulder and aretaining ring 175 threadedly engaged in the forward adaptor ringportion. Of course, either one or both filters 173 and 174 may beomitted if desired. Further, a sunshade (not shown) may be substitutedfor the filter 174 and retaining ring 175 and removably threaded in theforward adaptor ring portion 171. The adaptor ring 178 thus permits theoptional employment of one filter, two filters, or one filter and asunshade. In addition, the filter retaining ring 175 may be engaged inthe barrel portion 39 for holding a filter in the latter, if desired.

From the foregoing, it is seen that the present invention provides azoom effect accessory lens which fully accomplishes its intended objectsand is well adapted to meet practical conditions of manufacture and use.

Although the present invention has been described in some detail by wayof illustration and example for purposes of clarity and understanding,it is understood that certain changes and modifications may be madewithin the spirit of the invention and scope of the appended claims.

This application is a division of application Serial No. 551,302, filedDecember 6, 1955.

What is claimed is:

1. In a viewfinder for use with a zoom-effect lens, a barrel adapted tobe disposed longitudinally alongside of said zoom-effect lens, saidbarrel being formed with a through slot extending partiallycircumferentially of said barrel intermediate the ends thereof, saidbarrel being formed with an internal groove extending longitudinally ofsaid barrel, a bracket clamped about said barrel adjacent to and spacedfrom said slot and adapted for attachment to a zoom-effect lens,spur-gear means carried by said bracket on one side of the barrel foroperative connection to a zoom-effect lens, an external ring gearrotatably circumposed about said barrel in meshing engagement with spurgear, a pin carried by said ring gear and projecting radially inwardtherefrom through said barrel slot and interiorly of said barrel forrotation with said ring gear relative to said barrel, positive-lensmeans fixed 'in said barrel adjacent to each of its opposite ends, a

tubular lens mount longitudinally and slidably received in said barrel,said tubular lens mount being formed with a generally spiral cam grooveslidably receiving the projecting end of said pin, a second pinprojecting radially outward from said lens mount slidably into said1ongitudinal barrel groove to constrain said lens mount to longitudinalmovement in said barrel upon rotation of said ring gear, and a negativelens carried by said tubular lens mount for movement therewith towardand away from said respective positive lens means.

2. A viewfinder according to claim 1, said negative lens being carriedby said lens mount at one end thereof adjacent to one of saidpositive-lens means, said viewfinder also comprising a tubular bodypositioned longitudinally of and in spaced relation within said barreladjacent the opposite end of said barrel from the positive lens meansadjacent said negative lens, one end portion of said body extending intosaid lens mount, the other of said positive-lens means being mounted inthe end of said tubular body which is remote from said negative lens,said viewfinder also comprising a further negative lens in the endthereof which is proximate to said first mentioned negative lens, saidlens mount thus receiving said body to permit shifting of said firstmentioned negative lens into close proximity to the second mentionednegative lens.

References Cited in the file of this patent UNITED STATES PATENTS696,788 Allen Apr. 1, 1902 1,883,673 Fouquet Oct. 18, 1932 2,183,523Wood Dec. 19, 1939 2,377,821 Sperry et a1. June 5, 1945 2,537,561 WaittJune 9, 1951

